This invention relates to optoelectronics, and in particular to apparatus for control of the wavelength of emission from optical components.
In many optical systems, such as Wavelength Division Multiplexing (WDM) systems, tight control of the wavelength emission of components such as lasers is desired. A typical approach to stabilization is to collect light either from the front or back face of the laser, send it through a component whose transmission is a function of wavelength, and then compare the resulting beam to a reference beam. The ratio of the intensity of the two beams is kept constant by circuitry which controls the temperature of the laser or the electrical bias supplied to the laser.
While such solutions are generally acceptable, it is desired in some systems to eliminate the need for a reference beam.
The invention in one aspect is an optical apparatus including a first optical component emitting light at a desired wavelength and a second optical component optically coupled to the first optical component, the second component adapted to produce an optical output which is a function of the wavelength of the first component and of a voltage applied to the second component. A source of periodic voltage is electrically coupled to the second component. A photodetector is optically coupled to the second component so as to produce an electrical signal whose amplitude is a function of the voltage applied to the second component. A differentiation circuit is electrically coupled to the photodetector, the output of the differentiation circuit providing an error signal in the event that the light from the optical component differs from the desired wavelength.
The invention in another aspect is a method of controlling the wavelength of light emitted from a first optical component by directing the light through a second optical component which produces an output which is a function of the wavelength of the first optical component and of a voltage applied to the second component. A periodic voltage is applied to the second component, and the output is converted to an electrical signal whose amplitude is a function of the voltage applied to the second component. The derivative of the amplitude with respect to the voltage applied to the second component is determined and this derivative is used as an error signal to correct for any change in wavelength of light from a desired value.